Re: [PATCH v3] selftests: powerpc: Fix CPU affinity for child process

[Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>]

On Tue, Jun 09, 2020 at 01:44:23PM +0530, Harish wrote:
> On systems with large number of cpus, test fails trying to set
> affinity by calling sched_setaffinity() with smaller size for
> affinity mask. This patch fixes it by making sure that the size of
> allocated affinity mask is dependent on the number of CPUs as
> reported by get_nprocs().
> 
> Fixes: 00b7ec5c9cf3 ("selftests/powerpc: Import Anton's context_switch2 benchmark")
> Reported-by: Shirisha Ganta <shiganta@in.ibm.com>
> Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
> Signed-off-by: Harish <harish@linux.ibm.com>
> ---

Reviewed-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>

> v2: https://lore.kernel.org/linuxppc-dev/20200609034005.520137-1-harish@linux.ibm.com/
> 
> Changes from v2:
> - Interchanged size and ncpus as suggested by Satheesh
> - Revert the exit code as suggested by Satheesh
> - Added NULL check for the affinity mask as suggested by Kamalesh
> - Freed the affinity mask allocation after affinity is set
>   as suggested by Kamalesh
> - Changed "cpu set" to "affinity mask" in the commit message
> 
> ---
>  .../powerpc/benchmarks/context_switch.c       | 21 ++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/powerpc/benchmarks/context_switch.c b/tools/testing/selftests/powerpc/benchmarks/context_switch.c
> index a2e8c9da7fa5..d50cc05df495 100644
> --- a/tools/testing/selftests/powerpc/benchmarks/context_switch.c
> +++ b/tools/testing/selftests/powerpc/benchmarks/context_switch.c
> @@ -19,6 +19,7 @@
>  #include <limits.h>
>  #include <sys/time.h>
>  #include <sys/syscall.h>
> +#include <sys/sysinfo.h>
>  #include <sys/types.h>
>  #include <sys/shm.h>
>  #include <linux/futex.h>
> @@ -104,8 +105,9 @@ static void start_thread_on(void *(*fn)(void *), void *arg, unsigned long cpu)
> 
>  static void start_process_on(void *(*fn)(void *), void *arg, unsigned long cpu)
>  {
> -	int pid;
> -	cpu_set_t cpuset;
> +	int pid, ncpus;
> +	cpu_set_t *cpuset;
> +	size_t size;
> 
>  	pid = fork();
>  	if (pid == -1) {
> @@ -116,14 +118,23 @@ static void start_process_on(void *(*fn)(void *), void *arg, unsigned long cpu)
>  	if (pid)
>  		return;
> 
> -	CPU_ZERO(&cpuset);
> -	CPU_SET(cpu, &cpuset);
> +	ncpus = get_nprocs();
> +	size = CPU_ALLOC_SIZE(ncpus);
> +	cpuset = CPU_ALLOC(ncpus);
> +	if (!cpuset) {
> +		perror("malloc");
> +		exit(1);
> +	}
> +	CPU_ZERO_S(size, cpuset);
> +	CPU_SET_S(cpu, size, cpuset);
> 
> -	if (sched_setaffinity(0, sizeof(cpuset), &cpuset)) {
> +	if (sched_setaffinity(0, size, cpuset)) {
>  		perror("sched_setaffinity");
> +		CPU_FREE(cpuset);
>  		exit(1);
>  	}
> 
> +	CPU_FREE(cpuset);
>  	fn(arg);
> 
>  	exit(0);
> -- 
> 2.24.1
>